OneDimensionalFocusSearch.kt
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.ui.focus
import androidx.compose.ui.focus.FocusStateImpl.Active
import androidx.compose.ui.focus.FocusStateImpl.ActiveParent
import androidx.compose.ui.focus.FocusStateImpl.Captured
import androidx.compose.ui.focus.FocusDirection.Companion.Next
import androidx.compose.ui.focus.FocusDirection.Companion.Previous
import androidx.compose.ui.focus.FocusStateImpl.Deactivated
import androidx.compose.ui.focus.FocusStateImpl.DeactivatedParent
import androidx.compose.ui.focus.FocusStateImpl.Inactive
import androidx.compose.ui.node.ModifiedFocusNode
import androidx.compose.ui.util.fastForEach
import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.contract
private const val InvalidFocusDirection = "This function should only be used for 1-D focus search"
private const val NoActiveChild = "ActiveParent must have a focusedChild"
internal fun ModifiedFocusNode.oneDimensionalFocusSearch(
direction: FocusDirection
): ModifiedFocusNode? = when (direction) {
Next -> forwardFocusSearch()
Previous -> backwardFocusSearch()
else -> error(InvalidFocusDirection)
}
private fun ModifiedFocusNode.forwardFocusSearch(): ModifiedFocusNode? {
when (focusState) {
ActiveParent, DeactivatedParent -> {
val focusedChild = focusedChild ?: error(NoActiveChild)
focusedChild.forwardFocusSearch()?.let { return it }
// TODO(b/192681045): Instead of fetching the children and then iterating on them, add a
// forEachFocusableChild() function that does not allocate a list.
focusableChildren(excludeDeactivated = false).forEachItemAfter(focusedChild) { child ->
child.forwardFocusSearch()?.let { return it }
}
return null
}
Active, Captured, Deactivated -> {
focusableChildren(excludeDeactivated = false).fastForEach { focusableChild ->
focusableChild.forwardFocusSearch()?.let { return it }
}
return null
}
Inactive -> return this
}
}
private fun ModifiedFocusNode.backwardFocusSearch(): ModifiedFocusNode? {
when (focusState) {
ActiveParent -> {
val focusedChild = focusedChild ?: error(NoActiveChild)
when (focusedChild.focusState) {
ActiveParent -> return focusedChild.backwardFocusSearch() ?: focusedChild
DeactivatedParent -> {
focusedChild.backwardFocusSearch()?.let { return it }
focusableChildren(excludeDeactivated = false).forEachItemBefore(focusedChild) {
it.backwardFocusSearch()?.let { return it }
}
// backward search returns the parent unless it is the root
// (We don't want to move focus to the root).
return if (isRoot()) null else this
}
Active, Captured -> {
focusableChildren(excludeDeactivated = false).forEachItemBefore(focusedChild) {
it.backwardFocusSearch()?.let { return it }
}
// backward search returns the parent unless it is the root
// (We don't want to move focus to the root).
return if (isRoot()) null else this
}
Deactivated, Inactive -> error(NoActiveChild)
}
}
DeactivatedParent -> {
val focusedChild = focusedChild ?: error(NoActiveChild)
when (focusedChild.focusState) {
ActiveParent -> return focusedChild.backwardFocusSearch() ?: focusedChild
DeactivatedParent -> {
focusedChild.backwardFocusSearch()?.let { return it }
focusableChildren(excludeDeactivated = false).forEachItemBefore(focusedChild) {
it.backwardFocusSearch()?.let { return it }
}
return null
}
Active, Captured -> {
focusableChildren(excludeDeactivated = false).forEachItemBefore(focusedChild) {
it.backwardFocusSearch()?.let { return it }
}
return null
}
Deactivated, Inactive -> error(NoActiveChild)
}
}
// BackwardFocusSearch Searches among siblings of the ActiveParent for a child that is
// focused. So this function should never be called when this node is focused. If we
// reached here, it indicates that this is an initial focus state, so we run the same logic
// as if this node was Inactive. If we can't find an item for initial focus, we return this
// root node as the result.
Active, Captured, Inactive ->
return focusableChildren(excludeDeactivated = true)
.lastOrNull()?.backwardFocusSearch() ?: this
// BackwardFocusSearch Searches among siblings of the ActiveParent for a child that is
// focused. The search excludes deactivated items, so this function should never be called
// on a node with a Deactivated state. If we reached here, it indicates that this is an
// initial focus state, so we run the same logic as if this node was Inactive. If we can't
// find an item for initial focus, we return null.
Deactivated ->
return focusableChildren(excludeDeactivated = true).lastOrNull()?.backwardFocusSearch()
}
}
private fun ModifiedFocusNode.isRoot() = findParentFocusNode() == null
@OptIn(ExperimentalContracts::class)
private inline fun <T> List<T>.forEachItemAfter(item: T, action: (T) -> Unit) {
contract { callsInPlace(action) }
var itemFound = false
for (index in indices) {
if (itemFound) {
action(get(index))
}
if (get(index) == item) {
itemFound = true
}
}
}
@OptIn(ExperimentalContracts::class)
private inline fun <T> List<T>.forEachItemBefore(item: T, action: (T) -> Unit) {
contract { callsInPlace(action) }
var itemFound = false
for (index in indices.reversed()) {
if (itemFound) {
action(get(index))
}
if (get(index) == item) {
itemFound = true
}
}
}